In order to obtain a required driving torque and vehicle speed in a vehicle wherein an engine is mounted, an engine output is subjected to a speed change and transferred to a drive wheel by a transmission. A transmission mounted in the vehicle can be an automatic transmission, automatically setting an optimum speed-change ratio between the engine and the drive wheel, or a manual transmission. In contrast to an automatic transmission, a manual transmission has better fuel efficiency, acceleration, and deceleration.
In a vehicle wherein a manual transmission is mounted, a clutch is provided between the engine and the manual transmission, and by engaging or disengaging that clutch in response to an operation of a clutch pedal, an output torque of the engine is transferred to, or cut-off from, the manual transmission (for example, see Patent Document 1).
Meanwhile, port injection type engines and in-cylinder direct injection type engines are known as engines mounted in vehicles, etc. In a port injection type engine, a uniform air-fuel mixture is formed by injecting a fuel such as gasoline, etc. into an air intake path from a fuel injection valve (injector) provided in an air intake port, and the air-fuel mixture is introduced into a combustion chamber and ignited using a spark plug.
In an in-cylinder direct injection type engine, a fuel injection valve is provided in each cylinder, an air-fuel mixture is formed by injecting a fuel such as gasoline, etc. from that fuel injection valve directly into a combustion chamber and mixing with intake air introduced into the combustion chamber from an air intake port, and the air-fuel mixture is ignited using a spark plug. The in-cylinder direct injection type engine is superior in terms of low fuel consumption, low exhaust-gas emissions, and high output, etc., and therefore, demand is increasing rapidly.
Furthermore, in an engine mounted in a vehicle, an electronic throttle system comprising an actuator (throttle motor) driving a throttle valve provided in the air intake path and making it possible to control a throttle opening degree independent of an accelerator-pedal operation of a driver is known.
With the electronic throttle system, the throttle opening degree is controlled so as to acquire an optimum intake air volume (target air-intake volume) in accordance with driving states of the engine such as an engine rotation speed and a degree of accelerator-pedal depression of the driver (accelerator opening degree), etc. In specific terms, an actual throttle-opening degree of the throttle valve is detected using a throttle-opening degree sensor, etc., and an actuator of the throttle valve is subjected to feedback control such that that actual throttle-opening degree matches the throttle-opening degree (target throttle-opening degree) at which the above-mentioned target air-intake volume is acquired (for example, see Patent Document 2).    Patent Document 1: JP 2002-188658 A    Patent Document 2: JP 2002-021617 A    Patent Document 3: JP 2005-248909 A